Nitroparaffins having 1-3 carbon atoms and mixtures thereof, and particularly nitromethane, are known to be sensitizers for water gel explosives but some serious problems are encountered in producing separation stable water gel explosives using nitroparaffin sensitizers. Nitromethane is soluble to a certain degree, say 10 to 15%, in an aqueous phase. However, this concentration is seldom sufficient to achieve the desired sensitivity especially for cap sensitive compositions. Higher concentrations of nitromethane can be used to more effectively sensitize water gel explosive compositions. To achieve the higher concentrations or a more sensitive condition, the insoluble portion of the nitromethane must either be solubilized in the aqueous phase or suspended or dispersed therein by mixing it as very fine droplets in the overall aqueous gel structure of the explosive composition. When dispersing or suspending the nitromethane it is usually accepted that the finer the droplets, the higher will be the sensitivity factor.
In the case of the more fluid pourable and pumpable gels, the fine droplets of nitromethane have a tendency to coalesce into larger less effective droplets and to migrate until the insoluble nitromethane has effectively separated from the aqueous gel structure to form a separate layer. When this occurs, the overall composition becomes less sensitive and in most cases undetonable. This type of product is most unacceptable especially when the nitromethane sensitized explosive gel is poured or pumped through water which may cause the nitromethane to be separated from the aqueous gel structure more rapidly. Water attack on the aqueous gel structure accelerates this separation. Even stiff nonpourable or nonpumpable nitromethane sensitized gels show a tendency for the nitromethane to separate during storage.
In prior attempts to stabilize the nitromethane so that it resists coalescence and separation, various approaches have been taken. For instance, emulsifiers have been used for stabilizing the nitromethane, but the presence thereof appears to reduce the overall water resistance of such a composition. In storage, the separation shelf life of the emulsion-gel is directly related to the quality of the aqueous gel produced by the guar gelling agent, to the quality of the nitromethane emulsion as it is effected by the quality of the emulsifying agent, the size of the nitromethane dispersion and the mixing procedure.
Others have suggested the use of nitrocellulose as a gelling agent for the nitromethane but have failed to produce cap sensitive or higher sensitive compositions which indicates that high nitromethane concentrations or adequate dispersions were not even contemplated. In addition, a slower two-step process is taught for producing the composition wherein the nitroparaffin is first gelled after which it is combined by mixing with an aqueous oxidizer phase (Minnick U.S. Pat. No. 3,419,444). This necessarily means that the nitromethane gel will be dispersed in a variety of particle sizes throughout the aqueous phase rather than in the more desirable smaller droplets.
My copending patent application Ser. No. 593,307 filed July 7, 1975 teaches the simultaneous in situ gelation of the nitroparaffin and aqueous phases through the use of a gelling agent for the nitromethane and another gelling agent for the aqueous phase.
With regard to solubilizing the nitromethane, a nitromethane compound such as Tris (hydroxymethyl) nitromethane is used which is soluble in the aqueous phase of the composition or an alcohol is added to aid in making the nitroparaffin more soluble in aqueous gels (Minnick U.S. Pat. No. 3,419,444 and U.S. Pat. No. 3,409,485). However, once again booster systems are required to detonate these compositions and higher nitromethane concentrations are not contemplated. In addition, the U.S. Pat. No. 3,409,485 patent does not suggest the use of perchlorates and only a portion of the nitromethane in the composition is solubilized.
U.S. Pat. No. 3,765,967 discloses a water gel explosive composition wherein an alkali or alkaline earth metal perchlorate, e.g. sodium perchlorate, is used along with ethylene glycol, as an organic liquid fuel. There is no disclosure of the use of a nitroparaffin, particularly nitromethane, and if high sensitivity is desired other fuels such as particulate aluminum or explosives such as TNT, PETN or RDX are added.